[Cif2-encoding] A new(?) compromise position
James Hester
jamesrhester at gmail.com
Thu Sep 30 02:49:19 BST 2010
My simple objective (for files containing non-ASCII characters) is that an
application is able to determine the encoding of an incoming file with a
high degree of certainty with no information beyond the CIF standard, the
encoding standard, and the file contents. If the only choices are UTF8 or
UTF16 there is no danger of a misassignment of encoding. Furthermore, as
UTF8 files have a distinctive bit-pattern, non-UTF8 files can be reliably
detected(*). This appears to me to be an excellent state of affairs.
Although I have apparently restricted encodings to UTF8 and UTF16 in the
preceding paragraph, this is simply in an effort to get something workable
on the table that we can move forward with. I have no particular agenda to
limit in future the possible encodings for CIF files, provided that those
encodings can be reliably identified subject to the above restrictions.
Indeed, this particular group was formed in part to work out a system for
including those other encodings.
I realise my wordsmithing on the new proposal is somewhat lax, but if we are
in agreement on the principle I hope we are able to polish it up to
everybody's satisfaction.
James.
(*) John's email has addressed the UTF8 question in his post adequately, and
the wikipedia entry also contains useful discussion.
On Thu, Sep 30, 2010 at 3:00 AM, Herbert J. Bernstein <
yaya at bernstein-plus-sons.com> wrote:
> Dear James,
>
> I know from long and painful experience that files with just a few
> accented characters are very, very difficult to clearly identify, and can
> look like valid UTF8 files. UTF8 is _not_ self-identifying without the BOM.
>
> The case that really convinced me that there was a problem was a
> French document with a lower case e with an accent acute on the E. I
> nearly missed a misencoding of a mac native file that because it was being
> misread as a capital E in a UTF8 file showed the accent as grave.
>
> There are simply too many cases like that in which a file written in a
> non-UTF8 encoding looks like something reasonable, but wrong, to say that
> UTF without the BOM is self-identifying.
>
> As for the question of standards and applications, many programming
> language standards specify the action of processors of the language.
> In our case, to have a meaninful standard, we need to specify what
> is a syntactically valid CIF2 file, to specify the semantics for
> a compliant CIF2 reader and specify the required actions for
> a compliant CIF2 writer. We need to do so in a way that breaks
> as few existing applications as possible.
>
> I believe that applications are highly relevant to what we are trying to
> do. In particular, I favor strict rules on writers and liberal rules
> on readers, so that files get processed when possible, but tend to get
> cleaned up when being processed.
>
> That same frame of mind is why a lot of text editors invisibly add
> a BOM at the start of all UTF8 files, but try to accept UTF8 files
> with or without the BOM.
>
>
> Regards,
> Herbert
>
>
> =====================================================
> Herbert J. Bernstein, Professor of Computer Science
> Dowling College, Kramer Science Center, KSC 121
> Idle Hour Blvd, Oakdale, NY, 11769
>
> +1-631-244-3035
> yaya at dowling.edu
> =====================================================
>
> On Thu, 30 Sep 2010, James Hester wrote:
>
> Hi Herbert (I should be in bed, but whatever): I do not think it is
>> appropriate to require the *application* to unambiguously identify the
>> encoding, as no widely-recognised standard procedure exists to do this.
>> The
>> means of identification should rather be based on the international
>> standard
>> describing the encoding. Only UTF16 and UTF8 currently meet this
>> requirement, I believe. I will try to express this better after a
>> sleep...
>>
>> Regarding UTF8: I'm glad to see such vigilance in the cause of correctly
>> identifying file encoding. A UTF8 file, naturally, can also look like a
>> file
>> in a variety of single-byte encodings regardless of a BOM at the front.
>> However, a file in a non-UTF8 encoding is highly unlikely to be mistaken
>> for
>> a UTF8 file. Therefore, providing an input file is first checked for UTF8
>> encoding, I do not see any significant danger of a mistaken encoding. I'd
>> be happy to include recommendations to use a UTF8 BOM and to check for
>> UTF8
>> encoding before any others that we may eventually add to the list.
>>
>> I'm curious to see what these files are that you have trouble identifying
>> as
>> UTF8, as they may represent obscure corner cases. Any chance you could
>> dig
>> one or two up?
>>
>> James.
>> On Thu, Sep 30, 2010 at 12:45 AM, Herbert J. Bernstein
>> <yaya at bernstein-plus-sons.com> wrote:
>> Dear James,
>>
>> I respect the attempt to compromise, but the sentence "At
>> present only UTF8 and UTF16 are considered to satisfy this
>> constraint" is not quite
>> right without some additional work on the spec. UTF16 with a
>> BOM is
>> self-identifying. UTF8 with a BOM is also self-identifying.
>> However,
>> UTF8 without a BOM and without some other disambiguator (e.g.
>> the
>> accented o's), is _not_ self identifying. I know, because my
>> students
>> and I hit this problem all the time in working with
>> multi-linguage,
>> multi-code-page message catalogs for RasMol. Sometimes the only
>> way
>> we can figure out whether a UTF8 file is really a UTF8 file is
>> to
>> start translating the actual strings and see if they make sense.
>>
>> Another problem is what the "ASCII range" means to various
>> people.
>> I suggest being much more restrictive and saying "the printable
>> ASCII characters, code points 32-126 plus CR, LF and HT"
>>
>> Combined the statment I would suggest
>>
>> If a CIF2 text stream contains only characters equivalent to the
>> printable ASCII characters plus HT, LF and CR, i.e. decimal code
>> points 32-126, 9, 10 and 13, then to ensure compatibility with
>> CIF1, the CIF2 specification does not require any explicit
>> specification of the particular encoding used, but recommends
>> the use of UTF8. If a CIF2 text stream contains any characters
>> equivalent to Unicode code points not in that range, then for
>> any encoding other then UTF8 it is the responsibility of any
>> application writing such a CIF to unambigously specify the
>> particular encoding used, preferably within the file itself.
>> UTF16 with a BOM conforms to this requirement.
>>
>> Regards,
>> Herbert
>>
>> =====================================================
>> Herbert J. Bernstein, Professor of Computer Science
>> Dowling College, Kramer Science Center, KSC 121
>> Idle Hour Blvd, Oakdale, NY, 11769
>>
>> +1-631-244-3035
>> yaya at dowling.edu
>> =====================================================
>>
>>
>> On Thu, 30 Sep 2010, James Hester wrote:
>>
>> Here is a newish compromise:
>>
>> Encoding: The encoding of CIF2 text streams containing
>> only code points in the ASCII
>> range is not specified. CIF2 text streams containing any
>> code points outside the ASCII
>> range must be encoded such that the encoding can be
>> reliably identified from the file
>> contents. At present only UTF8 and UTF16 are considered
>> to satisfy this constraint.
>>
>> Commentary: this is intended to mean that encoding works
>> 'as for CIF1' (Proposals 1,2)
>> for files containing only ASCII text, and works as for
>> Proposal 4 for any other files.
>> I believe that this allows legacy workflows to operate
>> smoothly on CIF2 files (legacy
>> workflows do not process non ASCII text) but also avoids
>> the tower of Babel effect that
>> will ensue if non-ASCII codepoints are encoded using local
>> conventions.
>>
>> To explain the thinking further, perhaps I could take
>> another stab at Herbert's point of
>> view in my own words. Herbert (I think correctly)
>> surmises that all currently used CIF
>> applications do not explicitly specify the encoding of
>> their input and output files, and
>> so therefore are conceptually working with CIFs in a
>> variety of local encodings.
>> Mandating any encoding for CIF2 would therefore force at
>> least some and perhaps most of
>> these applications to change the way they read and write
>> text, which is disruptive and
>> obtuse when the system works fine as it is. Proposals 1
>> and 2 are aimed at avoiding
>> this disruption.
>>
>> On the other hand, I look at the same situation and see
>> that all this software is in
>> fact reading and writing ASCII, because all of these local
>> encodings are actually
>> equivalent to ASCII for characters used in CIFs, and I
>> further assert that this happy
>> coincidence between encodings is the single reason CIF
>> files are easily transferable
>> between different systems.
>>
>> These two points of view create two different results if
>> the CIF character repertoire is
>> extended beyond the ASCII range. If we allow the current
>> approach to encoding to
>> continue, the happy coincidence of encodings ceases to
>> operate outside the ASCII range
>> and CIF files are no longer easily interchangeable. If we
>> make explicit the commonality
>> of CIF1 encodings by mandating a common set of
>> identifiable encodings, the use of
>> default encodings has to be abandoned with accompanying
>> effort from programmers.
>>
>> I believe that this latest proposal respects Herbert's
>> concerns as well as mine, and is
>> eminently workable as a starting point for going forward.
>> I'm now off to do a sample
>> change and expect unanimous support from all parties when
>> I return in an hour's time :)
>>
>> On Wed, Sep 29, 2010 at 8:25 PM, Brian McMahon
>> <bm at iucr.org> wrote:
>> I think the crux of issue is as follows:
>>
>> [But part of our difficulty is that we are all having
>> separate
>> epiphanies, and focusing on five different "cruxes".
>> Clarifying
>> the real divergence between our views would be a
>> genuine benefit of
>> a Skype conference, to which I have no personal
>> objection.]
>>
>> In the real world, a need may arise to exchange CIFs
>> constructed in
>> non-canonical encodings. ("Canonical" probably means
>> UTF-8 and/or
>> UTF-16). Such a need would involve some transcoding
>> strategy.
>>
>> What is the actual likelihood of that need arising?
>>
>> I would characterise James's position as "not very,
>> and even less
>> if the software written to generate CIFs is
>> constrained to use
>> canonical encodings within the standard".
>>
>> I would characterise the position of the rest of us
>> as "reasonable to
>> high, so that we wish to formulate the standard in a
>> way that
>> recognises non-canonical encodings and helps to
>> establish or at
>> least inform appropriate transcoding strategies".
>> There appear to be
>> strong disagreements among us, but in fact there's a
>> lot of common
>> ground, and a drafting exercise would probably move
>> us towards a
>> consensus.
>>
>> Do you agree that that is a fair assessment?
>>
>> If so, we can analyse further: what are the
>> implications of mandating
>> a canonical encoding or not if judgement (a) is wrong
>> and if judgement
>> (b) is wrong? My feeling is that the world will not
>> end - or even
>> change very much - in any case; but it could
>> determine whether we
>> need to formulate an optimal transcoding strategy
>> now, or can defer
>> it to a later date.
>>
>> However, if anyone thinks this is just another
>> diversion, I'll drop
>> this line of approach so as not to slow things down
>> even more.
>>
>> Regards
>> Brian
>>
>> On Tue, Sep 28, 2010 at 09:28:25PM -0400, Herbert J.
>> Bernstein wrote:
>> > John,
>> >
>> > Now I am totally confused about what you are proposing
>> and agree with Simon
>> > that what is needed for you to state your proposal as
>> the precise wording
>> > that you propose to insert and/or change in the current
>> CIF2 change document
>> > "5 July 2010: draft of changes to the existing CIF 1.1
>> specification
>> > for public discussion"
>> >
>> > If I understand your proposal correctly, the _only_
>> thing you are proposing
>> > that differs in any way from my proposed motion is a
>> mandate that a
>> > CIF2 conformant reader must be able to read a UTF8 CIF2
>> file, but
>> > that _no_ CIF application would actually be required to
>> provide such
>> > code, provided there was some mechanism available to
>> transcode from
>> > UTF8 to the local encoding,
>> > which does not seem to be a mandate on the conformant
>> CIF2 reader at
>> > all, but a requirement for the provision of a portable
>> utility to
>> > do that external transcoding.
>> >
>> > If that is the case, wouldn't it make more sense to just
>> provide that
>> > utility that to argue about whether my motion requires
>> somebody to write
>> > their own? Having the utility in hand would avoid
>> having multiple,
>> > conflicting interpretations of this input transcoding
>> requirement.
>> >
>> > If I have read your message correctly, please just write
>> the utility you
>> > are proposing. If I have read your message incorrectly,
>> please
>> > write the specification changes you propose for the
>> draft changes
>> > in place of the changes in my motion.
>> >
>> > _This_ is why it was, is, and will remain a good idea to
>> simply have
>> > a meeting and talk these things out.
>> >
>> >
>> >
>>
>> --
>> T +61 (02) 9717 9907
>> F +61 (02) 9717 3145
>> M +61 (04) 0249 4148
>>
>>
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>>
>>
>>
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>> M +61 (04) 0249 4148
>>
>>
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